This application claims the priority of Korean Patent Application No. 2003-72138, filed on Oct. 16, 2003, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a flat lamp, and more particularly, to a flat lamp having a high brightness, a high luminous efficiency, and a uniform distribution of brightness.
2. Description of the Related Art
Flat lamps mainly used as back-light of liquid crystal displays (LCDs) have been developed into surface discharge type or facing surfaces discharge type lamps, in which the entire space under a light emitting surface makes a discharge space considering the luminous efficiency and uniformity of brightness, from conventional edge-light or direct-light type lamps using a cold cathode fluorescent lamp.
In general, the surface discharge type is advantageous in that a discharge characteristics is stable compared to the facing surfaces discharge type. However, the overall brightness of the surface discharge type is lower than that of the facing surfaces discharge type. As an example of a conventional surface discharge flat lamp, there is a lamp in which the overall discharge space is divided into fine discharge areas to prevent local concentration of discharge. This lamp can discharge stably. However, since the uniformity of the overall brightness is inferior due to a difference in the brightness and a gap between the fine discharge areas, a diffusing paper or diffusing plate is needed to uniformly diffuse light.
FIG. 1 shows another example of a conventional surface discharge type flat lamp. Referring to FIG. 1, discharge spaces filled with discharge gas are formed between an upper plate 20 and a lower plate 10 separated at a predetermined distance by a plurality of spacers 14.
A fluorescent layer 30 is formed on each of the inner surfaces of the upper and lower plates 20 and 10 and at both sides of the spacers 14. Pairs of electrodes including a first and second upper electrodes 22a and 22b and a first and second lower electrodes 12a and 12b are provided, respectively, on the outer surfaces of the upper and lower plates 20 and 10, which correspond to the respective discharge spaces. The first upper electrode 22a and the first lower electrode 12a facing each other maintain the same electric potential so that discharge is not induced therebetween. Also, the second upper electrode 22b and the second lower electrode 12b facing each other maintain the same electric potential so that discharge is not induced therebetween. Meanwhile, a predetermined electric potential difference is present between the upper electrode pair 22a and 22b and the lower electrode pair 12a and 12b so that discharge is induced between the electrode pairs in a direction parallel to the upper plate 20 or the lower plate 10.
In the flat lamps having the above structure, it is disadvantageous that since the first and second upper electrodes 22a and 22b on the upper plate 20 and the spacers 14 interfere light generated by a discharge, it is difficult to obtain uniform light. Also, when partial pressure of the discharge gas is increased, the discharge voltage highly increases.